Motorcycles manufactured by the Harley Davidson Motorcycle Company have achieved a celebrity status, acquiring a loyal following among motorcycle enthusiasts. Many of those enthusiasts customize their "Harley", placing their personal touch on the classic bike delivered by the manufacturer, whether by adding special paint, designs, chrome plating, accessories, and upgrading stock components with aftermarket equipment, acquired from the Harley Davidson Company or from independent equipment designers. Most such additions are intended to improve engine performance. The present invention also offers an aftermarket product that also addresses improving engine performance.
The internal combustion engine used in the Harley Davidson motorcycle in more recent years is a four stroke V-twin engine, referred to as the Evolution engine. That engine contains two cylinders and operates on the four stroke cycle of operation. Each engine cylinder contains a top portion, referred to as the cylinder head or simply as the head, containing the valves and associated inlet and exhaust ports and an internal cavity, the combustion chamber. As assembled, the head attaches atop the main cylinder containing the cylinder and piston, oriented with the combustion chamber aligned over the cylinder so as to complete the engine cylinder. In the stock Evolution big V-Twin engine, the combustion chamber is essentially hemispherical in shape, and is bordered by a straight side. The present invention in part addresses the cylinder head and, among other aspects, defines a combustion chamber of novel geometry.
Others earlier discovered that cylinder heads in stock Evolution engines incur considerable exhaust gas reversion during engine operation. As those skilled in the art understand, reversion refers to the movement of exhaust gases in the reverse direction, back up through the intake flow path. That effect essentially robs the engine of power that would otherwise be available from the charge of fuel. It is appreciated that internal combustion engines are designed to move gasoline vapors in one direction, through the intake as an air-fuel mixture, into the combustion chamber and, following combustion, from the combustion chamber as exhaust gases out the exhaust port. When instead exhaust gas reenters the combustion chamber and pollutes the air-fuel mixture, the nature of the combustible mixture is altered. The potential power of combustion that would otherwise be obtained from the fuel in the internal combustion process is reduced.
Many aftermarket designed replacement cylinder heads have been marketed as an upgrade to improve Evolution engine performance. A discussion of a variety of cylinder head designs offered by various companies to motorcyclists appears in an article entitled "Head Games" appearing at pages 55 through 59 of the January 1995 issue of Hot Rod Bikes magazine, Vol. 2, No. 1, which should be reviewed for possible background interest. It should be noted that the article was published subsequent to the present invention as that article includes the author's comment on the present invention as well.
One of those cylinder head designs, identified as the Gerolamy design, contains an enlarged combustion chamber and an enlarged intake port in which a side of the chamber wall is extended laterally away from the intake and exhaust ports a greater distance than the opposite chamber side to those ports. Although applicant does not know the theory behind the foregoing design, applicant believes the purpose underlying the design, like the others, is to increase turbulence of gases in the combustion chamber.
Accordingly, a principal object of the invention is to improve the four stroke engine, particularly to increase the level of power output and torque available from a given four stroke engine.
Another object of the invention is to reduce reversion of exhaust gases in internal combustion engines and thereby improve the efficiency of the engines' internal combustion.
A further object of the invention is to improve the performance of the Evolution V-Twin engine with a replacement cylinder head that reduces exhaust gas reversion to replace the cylinder head originally supplied with the engine.
An additional object of the invention is to provide a cylinder head for a four stroke motorcycle engine that minimizes occurrence of exhaust gas reversion and/or minimizes the effect of exhaust gas reversion in the operation of the motorcycle engine.
And still another object of the invention is to provide a new and improved motorcycle engine.